How to Build a Porch Roof

Jim HagertyUpdated February 21, 2017

Building a porch roof, once the initial steps of preparation have been taken, can be a job that can be done by yourself. Some useful information is all you need to avoid spending unnecessary money hiring a contractor.

When building a porch roof, evaluate your structures. The first step in building a roof on your porch is to determine if your porch and your home can withstand such an addition. Areas of rot and weak spots on your house or porch could spoil your project. It is important that your house is strong enough to hold the roof after it is attached.

Weak or rotted areas may make water and weatherproofing connection points difficult to create. Obstacles such as overhanging tree limbs, power lines and telephone poles must also be dealt with before you begin your porch roof. Some homes are not suited to support a porch with a roof.

Draw a blueprint. Although there might be some remodelling projects that may be completed without drawn plans, building a porch roof is commonly not one of them. Because you may be attaching the roof to the side of your house, an improperly-built structure can cause a sea of headaches. It is, therefore, crucial to have a concise drawing of your new roof. If you do not wish to consult an architect or drawing professional, there are several software programs that are able to create professional quality prints. Your print should also proper placement of electric outlets if you wish to run power to your porch, if it does not currently exist.

Note: When you are creating your blueprint, keep in mind that the roof on your house will ultimately determine how your porch roof will look. Your goal should be to match, as closely as possible, the pitch and shape of the roof of your home. Pay attention to overhang. A proper porch roof overhang should be between 12 and 14 inches.

Check to see if your porch is level. If it is not, you may need to raise it or lower it in spots that are throwing it off. Raising your porch be can done by jacking it up and filling in the gaps with additional dirt or concrete. If you are building a roof over a concrete slab that is not level, you may need to compensate by manipulating the lengths of your support posts.

Layout your support posts and other roofing materials. You may choose either square or round support posts to hold up your roof. The posts should be placed directly over support posts, if your porch is raised deck. Essentially, your roof supports will become extensions of your lower deck supports. It is crucial to install as many roof posts as your porch deck has deck supports. To fasten your posts to the deck, simply toenail them to the deck and brace them with 2X4s or bracing material. There are several ways in which this can be done. It is recommended that you use properly-sized post connectors, which can be purchased at most timber yards.

Note: It is crucial that your support posts are vertically plumb. If you are unable to level your deck, your roof still must be square and flush with your house. Again, this can be accomplished by manipulating the lengths of your posts to even everything out.

Install the top plate. Your top plate will be attached to your posts and form a box, to which your rafters will be attached. It is recommended that you use 4x8s for the top plate. Each board should be sanded and thoroughly cleaned. It is crucial to place each board on the posts correctly. Splices and joints should be directly over support posts and fastened with lag bolts.

Mark and install rafters. According to your blueprint, mark each location for the rafters. After each is marked, cut each rafter to length, leaving enough for proper overhang.

Note: If your porch is not perfectly square, do not cut each rafter the same length. This will result in rafters that are longer or shorter than others. Just as you did when installing your support posts, you again may be required to manipulate the length of your rafters if your porch isn't perfectly square.

Rafters should be temporarily toe nailed to your house and top plate with 10d nails. When each is placed and toe nailed, permanently fasten them with 8 to 10-inch spikes.

Cover your roof with Oriented Strand Board (OSB) or plywood. It is up to you how thick your sheathing will be, however, 1/2-inch is recommended. When covering your roof, it is important to make sure your insulation is compactly installed and the OSB fits properly. Roof sheathing should be nailed down with 5-1/2-inch panel screws. Your entire roof should be covered, including the overhang areas. After you have sheathed your roof, cap the ends of the overhanging rafters with 2x4s. To ensure that the overhang areas are capped properly, you may need to trim them so the 2x4 lay flush against the ends. Porch roofs need not be insulated.

Shingle your roof. The first step in shingling your new porch roof is to install flashing. Flashing should cover the small gap between the porch roof and your house. Secure flashing with nails and roof sealant.

Once you have installed flashing, you must weatherproof your roof deck. Weatherproofing simply involves applying a roll of underlay/felt which is made out of a rubber / tar composite. It is crucial that underlay/felt is smooth. Once you have weatherproofed your roof, install the shingles.

For your first row of shingles, lay a chalk line to ensure that your shingles are straight. If the first row of shingles is not straight, each successive row may be off, which may require you to trim excess material or add to empty spaces.

There is a large variety of shingles on the market. Some popular brands are CertainTeed, Owens Corning, Elk and GAF. To select the proper shingle for your porch roof, contact your local timber professional.

Tip

Obtain a permit/planning permission if needed. After you have properly drawn out your roof print, it is crucial to have it looked at by a building inspector.

Warning

Always use safety equipment when doing carpentry and homebuilding projects.

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About the Author

Jim Hagerty is a writer and journalist who began writing professionally in 1996. He has had articles published in the "Rock River Times," "Builder's Journal" and various websites. He earned a Bachelor of Science in public relations and journalism from Northern Michigan University in Marquette.